1. Field of the Invention
The present invention relates to a circuit for detecting high voltage level in MOS technology.
2. Description of the Prior Art
In a MOS integrated circuit, it is usually very difficult to precisely detect high voltage level, such as the supply voltage. This is because the transistor parameters are determined with a precision of about .+-.20%, which makes it very difficult to determine a reference voltage. Now, voltage sources are most often made with MOS transistors. Furthermore, the higher the voltage in question, the greater will be the number of variations in the reference voltage level. This is particularly troublesome with MOS integrated circuits such as EPROMs, EEPROMs or similar memories in which a certain voltage V.sub.pp is used for programming the cell and another voltage, usually the supply voltage V.sub.cc, is used for reading the cell. These memories are designed in such a way that they can be programmed with a voltage V.sub.pp of about 10 volts. If the read voltage V.sub.cc can reach this value, then the states of the memory cells can be changed. Hence the read voltage, namely the supply voltage, has to be limited to a precise value, which, in this case, is smaller than 10 volts.
The object of the present invention is to overcome these drawbacks by providing a circuit for detecting high voltage level in MOS technology, and for delivering a signal when the high voltage level exceeds a predetermined level. This signal may be used to turn off a circuit such as the read circuit in the case of PROMs or EEPROMs.